Cancer is a group of diseases caused by uncontrolled, unlimited growth of cells within a living body. Since cancer cells usually grow faster than normal cells, cancers would be capable of being treated by controlling the replication of DNA during the cell division, particularly during the division of chromosomes. Actually, gemcitabine, which has the effect of inhibiting DNA replication, is widely used in the treatment of non-small cell lung cancer, pancreatic cancer, biliary tract cancer, bladder cancer, breast cancer, ovarian cancer, or others.
Cdc7 is a serine-threonine protein kinase and is an enzyme which is essential for the initiation of DNA replication in the cell cycle. Specifically, Cdc7 forms a complex with cofactors such as Dbf4 (ASK), and phosphorylates its substrate, MCM (mini-chromosome maintenance) proteins. It is supposed that this phosphorylation results in assembly of Cdc45 and a DNA polymerase on the DNA to form an MCM complex, thereby initiating the DNA replication (see Non Patent Literature 1). Furthermore, it has been shown in a recent study that Cdc7 plays an important role not only in the replication of DNA, but also in DNA damaging pathways (see Non Patent Literature 2).
Recently, Cdc7 has drawn attention as a target of anticancer agents, and active researches on Cdc7 have been made. For example, it was found that CDC7 is overexpressed not only in common established cell lines derived from human tumors, but also in cells taken from live tissues, such as breast cancer, colon cancer, and lung cancer (see Non Patent Literature 3). Particularly, it was shown, in more recent days, that CDC7 is overexpressed in p53-mutated triple negative (ER−/PR−/Her2−) breast cancer cells (see Non Patent Literature 4), and thus it has been expected that Cdc7 will be a promising target molecule against a triple negative type of breast cancer, which has been considered to be difficult to treat. Actually, it was observed that in experiments for suppressing the expression of Cdc7 using RNA interference techniques, the arresting of the cell cycle was induced when the expression of Cdc7 was inhibited. More importantly, the Cdc7 inhibition using RNA interference techniques suppressed the growth of human tumor cells, such as HeLa and HCT116 cells, and exhibited only limited effects on normal cells (normal human skin fibroblasts) (see Non Patent Literature 5).
Therefore, selective inhibitors of Cdc7 can be expected to have an effective therapeutic effect against various types of cancer. Although various compounds having an inhibitory effect on Cdc7 have been reported in the past, there are no reports in which novel furanone derivatives of the present invention or pharmaceutically acceptable salts thereof have an inhibitory effect on Cdc7.